A Ray Tracing Solution to Diffuse Interreflection

by Greg Ward, Francis Rubinstein and Robert Clear

ABSTRACT

An efficient ray tracing method is presented for calculating
interreflections between surfaces with both diffuse and
specular components.
A Monte Carlo technique computes the indirect
contributions to illuminance at locations selected during the
rendering process.
The indirect illuminance values are averaged over surfaces
and used in place of a constant ``ambient'' term.
Illuminance calculations are made only for those areas participating
in the selected view, and the results are stored so that subsequent
views can reuse common values.
The density of the calculation is adjusted to maintain a constant
accuracy, permitting less populated portions of the scene to be computed
quickly.
Successive reflections use proportionally fewer samples,
which speeds the process and provides a natural limit to recursion.
The technique can also model diffuse transmission and
illumination from large area sources, such as the sky.

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